Topic Summaries

Plant diseases (HT ONLY)

IGCSE > Biology > CIE > IGCSE Biology Topic Summaries > Plant disease and monoclonal antibodies > Plant diseases (HT ONLY)
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Stem cells, microscopy, and microorganisms

Plant disease and monoclonal antibodies

The brain and the eye

Resource cycles and environmental change

Science skills: Measuring results

  • Symptoms of plant disease include: stunted growth, spots on leaves, rot (areas of decay), abnormal growths, malformed stem or leaves, discolouration, and pests.
  • Plant diseases can be identified by researching using a gardening manual or website, taking the infected plant to a laboratory to identify the pathogen, or using monoclonal antibody testing kits.
  • Plants can be infected by insects or viral, bacterial, or fungal pathogens.
    • Aphids are insects that tap into the phloem of plant stems with very fine mouthparts (stylet) to ingest the sap. This deprives the plant of its nutrient source. Plant growth rate decreases and the plant wilts. This can be prevented by increasing the number of ladybirds in your garden as they eat aphids, rather than spraying insecticides.
    • Tobacco mosaic virus: a viral disease transmitted by infected leaves rubbing against each other, resulting in a mosaic pattern of discoloured leaves. This affects many plant species (e.g. tomatoes) and affects their growth rate by reducing the rate of photosynthesis that can occur.
    • Black spot: a fungal disease that is transmitted by water or wind. It results in purple or black spots developing on leaves which are then more likely to turn yellow and fall/die. This affects the growth rate of the plant as photosynthesis is reduced, but can be treated using fungicides and removing/destroying the affected leaves so the disease cannot spread.
  • Plants can also be subject to nutrient deficiencies:
    • Mineral ions are absorbed from the soil by the roots.
    • Nitrate ions are needed for protein synthesis and therefore growth. Hence, nitrate deficiency causes stunted growth.
    • Magnesium ions are needed to make chlorophyll for photosynthesis. Therefore, magnesium deficiency causes chlorosis (yellow leaves).

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